Induction motor load relay system



Feb.4, 1947. m-1|." 2,415,189

INDUCTION MOTOR LOAD RELAY SYSTEM Filed May 19, 1945 3 Sheets-Sheet 1 E. PELL 2,415,189 INDUCTION IMOTOR LOAD RELAY SYSTEM Filed May 19, 1945 3 Sheets-Sheet 2 Patented Feb. 4, :1947

INDUCTION MOTOR LOAD RELAY SYSTEM Eric Pell, Shorewood, Wis., assignor to Cutler- Hammer, Inc., Mllwa of Delaware ukee, Wis., a corporation Application May 19, 1945, Serial No. 594,658

This invention relates to load relays and more particularly to load relays for induction motors. In practice a load relay to function within close limits and close to synchronous speed of the motor is often desired as for controlling transfer for control by the electrical condition of the motor secondary or rotor circuit.

Another object is to provide for a saturable reactor type of relay utilizing the motor rotor current for control of saturation, means for neutralizing the inductive effects which otherwise would impair its action and reliability.

Another object is to provide such a relay with means whereb it may be satisfactorily employed for a motor operating with its primary subjected to unbalanced voltages, as is highly desirable in hoist service where the motor is operating under overhauling load conditions.

Another object is to provide a relay which may be embodied in a number of specifically different forms.

Other objects and advantages of the invention will hereinafter appear.

Certain embodiments of the invention are illustrated in the accompanying drawings, and the same will now be described, it being understood that the invention is susceptible of embodiment in other forms without departing from the scope of the appended claims.

In the accompanying drawings: I

Figure 1 shows diagrammatically in conjunction with a motor one form of relay, but with- .out depicting any specific use of the relay.

Fig. 2 shows a modified form of relay in conjunction with a two-speed induction motor having separate sets of windings for its different speeds, the relay being depicted as employed for controlling transfer from one set of windings to another, and I Figs. 3, 4 and 5 depict certain characteristic curves hereinafter referred to. I

Referring to Fig. 1, the same shows schematically an induction motor M having its primary P supplied with power from alternating current suppl lines L L L through a. suitable main switch I and any suitable controller 2, such' for example as the now commercial controller for effecting motor reversals and unbalancing of the voltages to which the primary is subjected under 14 Clahns.- (Cl. 172-274) crating winding overhauling load conditions. The motor is shown as having in circuit with its secondary or rotor S resistors R R and R one for each phase of the circuit. which resistors are shown as being star connected. As will be understood, the controller 2 may comprise means for excluding the resistors R R and R in the usual manner when desired.

The relay .illustrated in Fig. 1 comprises a set of saturable reactors 5, 6 and I, one for each phase of the motor secondary circuit, and a second set of identical reactors 8, 9 and I0 coacting with the reactors 5, 6 and 1, respectively, to neutralize in their impedance coils undesired inductive effects when their saturating coils are supplied with a three phase alternating current. The reactors are employed to vary the impedance of a single phase circuit L; L supplied from lines L L respectively, and including a rectifier ll through which said single phase circuit supplies a sensitive'direct current switch or relay I 2 shown as of the normally closed type and having an opl3 connected to rectifier II by conductors l4 and I5. Preferably the rectifier H is of the full wave type and preferably it is paralled by a condenser I6, both provisions being advantageous for a more continuous supply of current to the winding l3.

As will be understood, the relay l2 may be employed for any of a number of different purposes including that depicted in Fig. 2. Thus in considering Fig. 1 the use made of the relay l2 will be neglected, but it will be assumed that it is desired to have the switch or relay l2 open when the secondary current of the motor exceeds a certain relatively low value, and to reclose only when the secondary current is reduced to a predetermined lower value such as that representing some desired change in operation, or a close approach of the motor to synchronous speed.

The several saturable reactors 5, 6 and I are of like form and except for having alternating current saturating coils are in general similar to the common form of saturable reactor having direct current saturating coils. Each reactor comprises a rectangular magnetic frame 20 with central leg 2| carrying the several coils of the reactor. Reactors 5, 6 and l are respectively provided with saturating coils 5, li and l, which coils are connected in the different phases of the motor secondary circuit, each in series with one of the resistors R R R These coils function to afford varying saturation of their respective magnetic frames for varying the imne ates! pedance value vof the coils 3 Ya l of reac= tors 5, B and I, respectively. The coils a, s and l are included in series in the single phase circuit L, H from which the direct current supplied to relay I2 is derived. The reactors ii,- a and l as thus far described would control the relay i2 similarly to the except for the undesired induced efiects of certain harmoniwof currents and fluxes resulting from supply of the coilsdt't and V with three phase alternating current, which as explained is the current of motor secondary circuit. I v

With the coils 59. E a l supplied with sinu= soidal currents, the peric alternat 1:: nun of reactors 5, d and l'will, ause of the non-linear permeability of the iron cores, take on a non= sinusoidal wave shape as shown in mg. 3. an analysis oi this flux wave'would-disclose composed of one fundamental sine wave and several higher odd harmonics. No even harmonics are present, unless the reactor cores possess residual magnetism. The first, third and fifth of these harmonics are depicted in Fig. 3 in relation to the total flux curve for a half cycle, as is the saturating current sine wave and the saturation curve from which the flux wave is constructed. Higher odd harmonics. although not individually shown are, of course, present in the flux wave.

The uctive effect of all these harmonics must he neutralized in the various coils of the reactors; The first harmonic and other odd har monies except the third and its multiples are neutralized by providing like reactors in the ditferent phases of the motor secondary. This is possible because the first harmonic comprises motor secondary amperes ttene out i s. l wer range or slip and some special proon is re'duired to-preserve for the" relay amperes a curve approximatingthat obtained under balanced mo= widely used in. o.-e. o. reactors it as three components displaced 12o degrees, whereby v the provision of a reactor for each of the t rec phases of the motor secondary results in cancelling out the efiects of this hiaonic on theseries connected impedance coils. All other odd harmonics which are not multiples of the third, 1. e., the fifth, seventh, eleventh, thirteenth, etc.,

are also neutralized by this connection since the.

components oi each are displaced 12% degrees, as depicted in Fig. 5. 0n the other hand. the third harmonic comprises components which are in phase and are not neutralized as in the cas of the first harmonic. However, the provision of the additional set of reactors t, 3 and ill affords a way of neutralizing such harmonic and multiples thereof. 4

The reactors 8, 9 and [It are like the reactors 5, t and l, but their impedance coils 8, er and it are 180 degrees out of phase with the impedance coils 5 6 and l of reactors it, and l, all oi said windings being connected in series relation.

The saturating coils e 9? and it are in series with the coils 5 B and i respectively, of reac= tors e, t and l, and with the arrangement de scribed it has been found that the third harmonic and its multiples are effectively neutralized to enable'very satisfactory control of the-impedance of the single phase current by saturation control of the reactors as a function of the vagcnrrent of the motor secondary or rotor circuit. As depicted in Fig. 4, it is possible to obtain within of relay shown in Fig. 1, andthe two impedance a low range of motor slip when the motor oper ates under balanced conditions or its pary an ammre curve for the relay it substantially par= alleling that of the motor amperes. 7

However, as depicted in Fig. d, where the motor primary is subjected to unbalanced voltages with a resultant negative sequence component of the secondary current to which the saturating wind= ings of the reactors are subjected, the curve oi tor primary conditions. Such provision can be made by use of additional coils t to it" on reactors 5 to H0, respectively, as illustrated. Coils 5, 5 and IF are connected in serieswith coils 839 and W, respectively, and the pairs or se= v ries connected coils are short=circuited in delta relation with impedances r r andvr These coils are subjected to induced voltages as a. function of the aforementioned negative sequence component of relatively high frequency and are utilized to buck outthe negative sequence saturating flux to substantially preserve the relay ampere curve as depicted in Fig. 4. Because oi its relatively low frequency the positive sequence component of the current and flux is not materially afiected by the aforementioned means employed to neutralize the eflects of the negative sequence component. As will be understood, the

bucking action of these additional coils will be' circuit or the high speed secondary circuit. The high and the low speed windings of the motor preferably are relatively non-inductive, l. 'e., the summation of the voltages induced in the various coils of one winding by the flux of the other winding is zero at the terminals of the unexcited winding.

. Each of reactors 25, 26 and El comprises a magnet frame similar to those of Fig. l, but in this instance only the saturating and neutralizing coils are mounted on the center leg, the im- "pedance coils being mounted on outside legs. The three reactors have saturating coils 25 28 and 'zll respectively, for inclusion in the slow speed secondary circuit of the motor, and with saturating coils 25 26 and El, respectively, for con nection in the high speed secondary circuit oi the motor. The coils 25 26 and Ell are respectively connected in series with resistors R R and R which are star connected, while the coils 26 se and El are respectively connected in series with resistors R", 1d. and R which are also star connected. The neutralizing coils 2E5, Et and 2l have connections similar to those of Fig. 1, in elusive of delta connected impedances r 1' and T In this instance the reactors 25, 2e and 2? are respectively provided with two impedance coils 25-25 lt -26 El -Zi each pair of these coils being mounted on the outer legs of the respective magnetic frame. All impedance coils of the three reactors are connected in series relation in a single phase circuit as in the form coils of each reactor are connected in a bucking relation. Thus each reactor may be likened to any one of the main reactors of Fig. 1, plus the corresponding additional reactor having its impedance coil in a bucking relation to that of the corresponding main reactor, and as a consequence each dual reactor of Fig. 2 will inherently tendto neutralize the third harmonic and all multiples the" motor secondary,

I nected in the diiferent phases ondary S.

vice responsive to load thereof. As in Fig. l, the inductive eiiect oi the first harmonic'and all higher odd harmonics not multiples of the third is neutralized by providing three of the dual reactors, one for each phase of and the coils 25, 26 and 21 will neutralize, as in Fig. 1, the undesired fluxes resulting from operating the motor under 1 unbalanced primary voltages.

each reactor has two saturating coils, said coils function selectively for low speed and high speed operation of the motor, wherefore this arrangement can be said to save three magnetic frames and three reactor coils as compared with the arrangement of Fig. l.

The single phase circuit including the impedance coils is like that shown in Fig. 1 and has been given the same reference characters, as have also the. double wave rectifier II, the relay l2 and condenser l8. In this instance the normally closed contacts l2 of relay l2 are'shown as employed to control the operating winding of a selector switch 30 for the slow and high speed windings of motor M The switch 30 when deenergized selects the motor slow speed primary, and when energized selects the motor high speed primary, said switch being under the control of relay l2 jointly with master switch contacts 3|.

The master switch is assumed to be' of the drum type movable from on? position in opposite directions selectively, and said contacts 3| are normally, disengaged subject to engagement only when the master switch is moved to extreme positions indicated by the crosses on certain of the broken lines indicating positionsof the master switch when moved to either side of oil! position.

Thus the slow speed motor primary is selected for starting and relay l2 responds upon starting to prevent selection of the high speed primary of the motor until the master switch it is closed, and until the relay l2 recloses as themotor approaches its slow synchronous speed, or when the load as measured by the secondary current assumes some predetermined value selected as safe for transferring to the high speed winding.

- While further description of Fig. 2 is believed unnecessary, it may be pointed out that the motor slow speed windings comprise windings P and S while its high speed windings comprise windi-rigs P and S", the switch 3| ailording selection of the windings P? and P; Also there is shown for control 01' the motor primary a main switch 32 and in outline a suitable control panel 33 which may if desired comprise reversing means for the motor primary and unbalancing means for the motor primary, all under the control of the master switch of which the contacts 3i form a part. As will be apparent without tracing the circuits, the reactor coils 25, 26 and 27 are included in diflerent phases of the motor secondary S while the coils 25", 28 and 2! are con- What I claim as new and desire tosecure by Letters Patent is:

1. In combination, an induction motor, an elec- 85 tro-responsive device, means rendering said deon said motor, said means comprising a control circuit for said device, and saturable reactor means subjected to the rotor current of said motor for varying saturation and device, means rendering said de- While in Fig.- 2

of the motor secnarrates comprising a control circuit for said device, and

saturable reactor means subjected to the rotor current of said motor for varying saturation and 5' afl'ording as .a function of varying saturation a varying impedance in the control circuit for said device, said saturable reactor means substantially neutralizing undesired in duced fluxes, thereby to cause said saturable reactor means to simulate the impedancevarying action of saturable-reactor means supplied with direct current for varying saturation.

3. In combination, an induction motor, a sensitive electroresponsive device, means rendering said device responsive to load on said motor, said means comprising a control circuit for said device, and saturable reactor means subjected to the rotor current of said motor for varying satuafl'ording as a function of varying saturation a varying impedance in the control circuit for said sensitive device, said saturable reactor means comprising neutralizing means for.

induced fluxes thereby device sensitive to load value when said motoris operating close to synchronous speed.

4. In combination, an induction motor, an elecincluding a rectifier through which said electrovice, and saturable reactor means subjected to the rotor current of said motor for varying saturation and ailording as a function of varying saturation a varying impedance in said control cirsaturable reactor means comprising'a plurality of like component parts individualized to the diiIerent phases of themetor secondary circuit in respect of their saturating coils and having their impedance coils connected in series 7. In combination, a pblyphase induction motor, an electroresponsive device for response to load on said motor, a control circuit for said.device, and saturable reactor means subjected to the rotor current of said motor for varying saturation and affording as a function of varying saturation a cuit of said device, said saturable reactor means to the difl'erent phases of the motor secondary circuit in respect of their saturatmeans comprising to render said varying impedance in said contr'ol cir-- 7 ing coils and having their impedance coils all connected in series, with a pair of impedance coils for each phase of the motor secondary circuit in bucking relation.

8. .In combination, troresponsive device for-response to load on said motor, a control circuit for saiddevice, and saturable reactor means subjected to the rotor curan induction motor, an elecrent of said motor for varying saturaton and affording as a function of varying satuiation a varying impedance in said control circuitfor said device, said saturable reactor means comprising neutralizing means for the flux produced therein as a function of negative sequence flux resulting from operation of said motor with its primary subjected to unbalanced voltages.

coils and having their impedance coils all con-' nected in series, with a pair of impedance coils for each phase of the motor secondary circuit in trical condition of said circuit, said means com prising'a control circuit for said device, and saturable reactor means sub ected to the current of said circuit for'varying saturation and affordin as a function of varying saturation a varyi inpedance in said control circuit for said device, said saturable reactor means comprising like component parts individualized to the diflerent phases of said circuit in respect of their saturating coils, and each of said component parts having a pair of bucking impedance coils connected in series with one another and with the corresponding coils of the other component parts of said saturable reactor means.

12. In combination, a polyphase alternating current circuit, a single phase alternating current circuit including a double wave rectifier, an electroresponsive device supplied with direct current from said single phase circuit through said rectifier, a plurality of saturable reactors having their impedance coils in series in said single phase bucking relation, and said saturable reactor means i also comprising neutralizing means for the flux produced therein as afunction of negative sequence flux resulting from operation of said motor with its primary subjected to unbalanced voltages. i

10. In combination, a;polyphase alternating current circuit, an electroresporisive device, means rendering said device sensitive to the electrical condition of said circuit, said means comprls-' ing a control circuit for said device, and saturable reactor means subjected to the current of said circuit, there being a saturable reactor for each phase of said polyphase circuit and each such reactor having a saturating coil subjected, to the current of its respective phase of said polyphase circuit.

13. In combination, current circuit, a single phase alternating current circuit including a double wave rectifier, an electroresponsive device supplied with direct current from said single phase circuit through said rectifier, a plurality of saturable reactors having their impedance coils in series in said single phase circuit, there being a saturable reactor for each phase of said polyphase circuit and eachsuch reactor having a pair of impedance coils in bucking relation and a saturating coil subjected to the current of its respective phase of said polyphase circuit.

circuit for varying saturation and affording as a function of varying saturation a varying impedance and consequent current control in said control circuit for said device independent of frequency of said polyphase circuit, said saturable.

reactor means comprising like component parts cuit in respect of their saturating coils and having their impedance coils in series relation.

11. In combination, a polyphase alternating current circuit, an electrorepsonsive device, means rendering said device sensitive to the elec- 14. In combination, a polyphase alternating current circuit, a single phase alternating cur-' rent circuit including a double wave rectifier, an electroresponsive device supplied with direct ourrent from said single phase circuit through said individualized to the diiierent phases of said cirrectifier, a plurality of saturable reactors having their impedance coils in series in said single phase circuit, there being a double saturable reactor for each phase of said polyphase circuit, the component parts of each having their impedance coils in opposed relation and having series ccnnectedsaturating coils subjected to the current of their respective phase of said polyphase circuit.

mo FELL.

a" polyphase alternating 

